Liquid circuit breaker



Patented July 21, 1942 LIQUID CIRCUIT BREAKER Joseph Slepian, Pittsburgh, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 28, 1939, Serial No. 311,356

7 Claims. (Cl. 200-144) This invention relates to improvements in circuit interrupters and, more particularly, to liquid circuit breakers using slightly conducting liquid, such as water.

In breakers of the aforesaid type it is desirable to have one of the contacts completely out of the liquid when the breaker is in the open circuit position because of the losses due to the low dielectric strength of the liquid under continued voltage application. However, tests on water breakers reveal that breakdown through the water often occurs during the closing operation resulting in considerable explosive effects. Such breakdowns appear to occur when the moving contact is close to, but not yet submerged below the surface of the liquid. A probable explanation of this behavior is that when the contact approaches the water surface, the high dielectric constant and conductivity of the water compared to the similar quantities for the series air gap results in practically the full circuit voltage being applied across the air gap. The overstressed air breaks down and arcs to the water whence the current is conducted to the submerged contact. However, after the air is ionized, its effective dielectric constant approaches infinity and hence there is an electrostatic force tending to draw the arc into the liquid. This action forces the liquid, out of the path between the contacts, completing the breakdown. For this reason, it is evident that breakdown is particularly likely in closing operations as the moving contact approaches the water surface or in opening operations, after the moving contact has been drawn out of the water.

The object of this invention, therefore, is to provide an improved breaker of the slightly conducting liquid type wherein breakdown through the liquid is prevented during the closing or opening operation.

A more specic object of the invention is to provide a metallic shield near the surface of the conducting liquid of a liquid breaker for arresting the electrical discharge normally occurring between the moving contact and the liquid during either the opening or closing operation of the breaker.

Other objects and advantages will appear from the following description taken in connection with the accompanying drawing, in which:

Figures 1 and 2 schematically illustrate two successive stages of the electrical phenomenon that takes place during the closing operation of a water breaker of the prior art; and

Fig. 3 illustrates a circuit interrupter embodying the principles of my invention.

` In order to more fully understand the electrical phenomenon which takes place during the opening and closing operation of a simple water breaker, reference may be had to Figs. 1 and 2 in which the reference numeral 5 designates a cylindrical container of insulating material having upper and lower metallic closure members I and 9. The upper closure member 'I is provided with an aperture II through which a movable contact I3 is adapted to operate. 'I'he contact I3 co-acts with a tulip type contact I5 mounted on the lower closure member 9. The closure 5 may be partly filled with slightly conducting liquid I1, such as water so as to provide an air space between the liquid and the upper closure member 'I.

It has been found that when the moving contact I3 is in the position as shown in Fig. 1, that is, a short distance above the surface of the liquid II, the liquid has a much lower dielectric strength than when the contact I3 is in actual contact with the liquid. 'I'his makes it diilicult to close an interrupter of this type since an arc strikes while the contacts I3 and I5 are still separated a great distance and the gas developed as a result of the arc is a handicap to immediate reopening of the interrupter.

The explanation of the low dielectric strength of the liquid with a series air gap may be the following: When the contact I3 approaches the liquid surface the air breaks down, passing the leakage current of the liquid which may be many amperes. With this current through it the air above the liquid will become more conducting than the liquid and an arc forms through the air as shown at I9 in Fig. 1. Under these conditions the air thus rendered conducting is pulled 40 by the electrostatic forces into the stronger parts of the electric field between the contacts I3 and I5 and tends to elongate parallel to the field. Thus, the conducting air strikes down through the liquid and causes electrical breakdown as shown at 2l in Fig. 2. This breakdown continues until an arc is established between the contacts I3 and I5. It will, of course, be understood that the same electrical phenomenon may take place during the opening operation of a water breaker when the moving contact is being withdrawn from the surface of the liquid. In order to overcome the electrical breakdown of the liquid in a circuit interrupter, an improved structure has been provided as more clearly shown in Fig. 3.

In this figure, the reference numeral 23 designates an outer casing member of insulating material having a metallic ange member 25 secured to the lower end thereof. The lower end of tubular casing 23 is closed by the spherical metallic member 21 which may be clamped to the flange 25 in any well known manner. Held in clamping engagement between the ange 25 and the closure member 21 is a contact supporting plate 29 which extends transversely across the lower end of the casing member 23. 'I'he support plate 29 carries a hollow metallic support 3| within which are yieldingly supported a plurality of contact fingers 33. Access to the contact fingers 33 is had through an opening 35 in the upper end of the hollow supporting member 3|. Resting upon the support plate 29 is a spacing sleeve 31 of insulating material which extends upwardly within the casing 25 and carries a metallic shield member 39, the purpose of which will be explained more fully hereinafter.

The shield member 39 is held against upward movement by a spacing sleeve 4|, also of insulating material, which bears against the lower side of a cap member 43 secured to the upper end of the casing 23. A movable contact rod 45 is mounted for reciprocating movement through an aperture 41 in the cover member 43 and an aperture 49 in the shield member 39 so as to coact with the contact lingers 33. The contact rod 45 may be operated into and out of contacting engagement with the contact iingers 33 by a suitable operating mechanism, only a part of which is shown at 5|. When the contact rod 45 is in engagement with the contact fingers 33, an electrical circuit ,is established through the interrupter from a terminal 53 secured to the contact rod, the contact rod 45, Contact fingers 33, hollow casing 3|, supporting plate 29, flange 25, and a terminal 55 carried by the flange 25. The casing 23 is preferably filled with slightly conducting liquid 51 such as water to the level shown.

In order to interrupt the circuit the operating mechanism 5| withdraws the moving contact 45 and circuit interruption takes place in the usual and well known manner. The moving contact 45 is preferably moved a considerable distance above the surface of the liquid so as to provide adequate insulation in air when the interrupter is in the open circuit position. The contact rod 45 may also be completely withdrawn from the casing 23 in the event that a higher factor of safety is desired.

In order to prevent electrical breakdown between the moving contact 45 and the surface of the liquid 51, the shield member 31 previously mentioned is disposed adjacent the surface of the liquid. This shield member has an annular cutaway portion 59 immediately below the aperture 49 to provide a flange portion 60 spaced above the surface of the liquid. The liquid in the casing 23 is maintained at a level so that the air gap between the flange 60 and the surface of the liquid is always greater than the clearance between the contact rod and aperture 49. Thus, during the closing operation, as the contact rod 45 approaches the shield member 39, the air breaks down between the shield member 39 and the contact rod to establish a spark or arc as shown at 6|. A conducting path is established between the contact rod 45, the shield member 39, and the liquid 51, thereby preventing the initial discharge to take place between the contact rod 45 and the surface of the liquid 51. The air between the liquid and the contact 45 therefore retains its resistance and is not pulled into the liquid. Even though a discharge does take place in the air just before the contact 45 touches the surface of the liquid, the eld at that point is very much weaker than in the case illustrated in Fig. 1, so that the motion of conducting gas down into the liquid will be slower than the motion of the electrode and', consequently, is quickly by-passed by the moving contact rod during it movement toward the contact fingers 33.

It will, of course, be understood that the shield member 39 is also effective to by-pass an electrical discharge which would normally occur between the surface of the liquid 51 and the moving contact 45 during the opening operation of the interrupter since the clearance between the contact rod 45 and the shield member 39 is less than the air gap between the surface of the liquid and the portion of the shield surrounding the aperture 49.

Although I have shown and described a specific embodiment of my invention, it is to be understood that the same is for the purpose of illustration and that changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the appended claims.

I claim as my invention:

l. In a circuit interrupter, a quantity of arc extinguishing liquid of the partially conducting type, separable contacts at least one of which remains immersed in said liquid during the circuit interrupting operation, operating means for withdrawing at least another of said contacts from said one contact and said liquid to interrupt the connected circuit, and shield means adjacent the region of departure of said movable contact from said liquid and arranged with respect to the path of movement of said movable contact to cause electrical breakdown between said movable contact and said shield means thereby preventing electrical breakdown between said liquid and said movable contact.

2. In a circuit interrupter, a quantity of slightly conducting arc extinguishing liquid, separable contacts immersed in said liquid at least during normal current carrying conditions of said interrupter and during the initial separation thereof, means for operating one of said contacts into and out of engagement with another of said contacts and into and out of said liquid, and a shield member adjacent the surface of said liquid and so arranged with respect to said one contact to provide a conducting path between said contact and said shield member to prevent electrical breakdown between said one contact and said liquid as said contact either approaches or recedes from said liquid.

v3. In a circuit interrupter, a container, slightly conducting arc extinguishing liquid partially filiing said container, coacting contacts normally immersed in said liquid, at least one of said contacts being movable to establish an arc in said liquid, operating means for moving said movable contact into and out of said liquid, and a metallic shield member in contact with said liquid and adjacent the surface of said liquid, said member of conducting material having a portion thereof in contact with said liquid and another portion out of contact therewith but spaced from the path of movement of said moving contact to establish a conducting discharge path between said movable contact and said member of conducting material so as to prevent electrical breakdown in air from said moving contact to said liquid during either the circuit opening or closing operation.

5. In a circuit interrupter, arc extinguishing means including a container, said container having a quantity of slightly conducting liquid therein and a space above said liquid, a stationary contact immersed in said liquid, a coacting movable contact, means for moving said movable contact to open and closed circuit positions, said movable contact being separated by a substantial gap from the surface of said liquid when in the open circuit position, and a shield member of conducting material disposed across the surface of said liquid and in contact therewith adjacent the surface thereof only, said shield member having an opening therethrough for the passage of said moving contact and an annular portion around said opening out of contact with said liquid for causing the electrical discharge from said movable contact to pass to said liquid through said annular portion during either the circuit opening or closing operation.

6. In a circuit interrupter, an arc chamber having a quantity of partially conducting liquid therein, relatively movable contacts separable Within said liquid, at least one of said contacts being operative into and out of said liquid and being positioned a substantial distance from the surface of said liquid when in the open circuit position, and a metallic shield member having a portion thereof in contact with said liquid adjacent its surface, said shield member being insulated from both of said contacts except for any slight conduction through said liquid when said contacts are in the open circuit position, and said shield having a portion closely adjacent said one contact just prior to movement of said one contact into engagement with the surface of said liquid and said portion being out of engagement with said liquid.

7. In a circuit interrupter, an arc chamber having a quantity of partially conducting liquid therein, relatively movable contacts separable Within said liquid, actuating means for said contacts operative for moving at least one of said contacts into and out of said liquid, said one movable contact when in the 'open circuit position being separated from said liquid by a gap capable of withstanding high voltage and a metallic shield member in contact with said liquid adjacent the surface thereof only and having a portion out of contact with said liquid but disposed close to the path of movement of said movable contact just prior to movement of said movable contact into engagement with the surface of said liquid.

` JOSEPH SLEPIAN. 

